Non-return valves are common in industrial and domestic applications and are particularly prolific on pneumatic tyres. A conventional valve typically comprises an inlet casing which is screw threaded within a valve stem of a tyre. The inlet casing houses a shaft along which a valve member slidably moves. The valve member is biased against a seat of the casing under the force of a compression spring so as to close the valve. Such a conventional valve comprises a relatively large number of components, is relatively expensive and complicated in operation.
The applicant discloses in international patent application WO 00/77429 a non-return valve which comprises a conical-shaped diaphragm in a fluid passage way. The diaphragm has a collapsible aperture which has an apex that is orientated in a forward flow direction. The diaphragm itself initiates closure of the collapsible aperture and the closure is further promoted by fluid on the high pressure side of the valve to thus prevent fluid flowing in a reverse direction. When pressure is applied to an inlet side of the diaphragm, the diaphragm deflects to expose the aperture and allow fluid to flow through the passageway from the inlet to the outlet only.